Conventionally, in a semiconductor manufacturing process, it is required to perform several different kinds of processings such as, for example, a heat treatment, a film forming processing and an etching processing, repeatedly on a semiconductor wafer (hereinafter, simply referred to as a “wafer”). Since such various processes are often performed in different processing apparatuses, it is required to transfer the wafer among processing apparatuses. Accordingly, in order to prevent adhesion of foreign substances or formation of a natural oxide film on the surface of the wafer when the wafer is transferred, the wafer is stored in a substrate storage container (wafer carrier) which is called a front-opening unified pod (FOUP), and is transferred in a state where the degree of cleanliness in the container is maintained at a certain level. The FOUP includes a container in which a plurality of semiconductor wafers may be placed horizontally, and a cover provided on the front side of the container. The cover is provided with a locking mechanism such that the semiconductor is hermetically stored.
Meanwhile, each processing apparatus that performs a processing on wafers is formed with a transfer port so as to carry the wafers stored in the FOUP into the processing apparatus. The transfer port is opened/closed by an opening/closing door pursuant to the front-opening interface mechanical standard (FIMS). The opening/closing door is provided with a cover opening/closing mechanism configured to remove a cover provided on the front side of the FOUP. That is, the opening/closing door is required to play a role to open/close the cover so as to deliver the wafers between the FOUP and a wafer transfer region in the processing apparatus, as well as a role to isolate the wafer transfer region from a carrier transfer region so as to maintain the wafer transfer region at a low oxygen concentration.
A process of removing the cover will be described in detail. The cover opening/closing mechanism moves forward to the cover of the FOUP in a state where the front surface of the FOUP comes in close contact with the transfer port of the processing apparatus, and acts on the locking mechanism provided on the cover to release the locking. Then, the cover opening/closing mechanism is moved backward to the wafer transfer region side in the processing apparatus while holding the cover in which the locking is released such that the wafers in a carrier are opened to the wafer transfer region. When the FOUP is opened, nitrogen gas is purged into a space between the opening/closing door and the FOUP such that an internal atmosphere of the FOUP is substituted with the nitrogen gas. As such, the wafers carried out of the FOUP are not exposed to oxygen, and carried into the apparatus in a state where no oxygen gets in the processing apparatus.
However, when the FOUP is carried into various processing apparatus, in some cases, the FOUP may be installed just in the transfer port and carried into the wafer transfer region of the processing apparatus, or the FOUP may be first kept on the container keeping rack which is called a stocker where the FOUP is placed. Generally, in a processing apparatus that performs a batch processing, in order to process wafers stored in a plurality of FOUPs at once, the plurality of FOUPs are first stored in the stocker and installed successively alternatively in the transfer port to carry the wafers into the wafer transfer region by the number of sheets to be processed at one time. Accordingly, when the stocker is on standby, the wafers may be hermetically stored in the FOUPs so as to maintain the degree of cleanliness at a certain level. Further, when the FOUPs are transferred to the wafer transfer region, the FOUPs may be carried immediately into the processing container to be subjected to the processing. Accordingly, it is possible to perform the processing while maintaining the wafers in a clean state.
Further, as for a substrate processing apparatus using such a stocker, there is known a substrate processing apparatus having a configuration in which after a nitrogen gas inlet port provided in the bottom plate of an FOUP cassette is fitted in a nitrogen gas supply port on a rack plate, nitrogen gas flows into the FOUP cassette from the nitrogen gas supply port such that the FOUP cassette is filled with the nitrogen gas such that a nitrogen substitution is performed in the FOUP even when the FOUP cassette is on standby on the rack plate of the cassette rack (stocker). See, e.g., Japanese Patent No. 4308975.
By such a configuration, the degree of cleanliness in the FOUP may be maintained by performing the nitrogen substitution in the FOUP even when the FOUP is on standby on the stocker.